I think that the guard over the tomb of the unknown soldier should have a loaded weapon. Chrome and polish it all you want. Heck, polish the cartridges if you want. But it should be an operational, loaded weapon and the Soldier should have a reasonable ROE. I think police officer level engagement unless attempting to deface/damage tomb. Then the perp gets enemy status and military shoot on sight. I think that the ceremonial honor guard for the flag should be the same way. Chrome the 1917 all you want, but it should be operational and loaded.
My bases have at least always issued live ammo and firearms to auxillery guards, even during exercises. You see a person with a M16 or M9, and you can count on it having a loaded magazine (if not one in the chamber).